PENGANTAR TEKNIK ELEKTRO TELEKOMUNIKASI II AGNES STANDAR KOMPETENSI Mahasiswa mampu memahami konsep dan persamaan dasar bidang telekomunikasi RUJUKAN Tarmo Anttalainen, Introduction to Telecommunications Network Engineering, 2003 A COMMUNICATIONS MODEL COMMUNICATION SYSTEMS Basic Digital Communications System Baseband audio video (analogue) Source Channel Code A/D anti-alias filter •Nyquist sampling •FEC •ARQ •block •convolution Source code data (digital) Passband pulse shaping filter •ISI •ASK Modulation •FSK •PSK •binary •M’ary Communications Channel Transmit •loss •interference •noise •distortion Receive data (digital) Source decode Sink audio video (analogue) channel filter D/A low pass filter quantisation noise Channel Decode Regeneration •matched filter •FEC •decision threshold •ARQ •timing recovery •Block •Convolution Demodulation •envelope •coherent •carrier recovery channel filter COMMUNICATION CHANNELS A channel is a path between two communication devices Channel capacity: How much data can be passed through the channel (bit/sec) Also called channel bandwidth The smaller the pipe the slower data transfer! Consists of one or more transmission media Materials carrying the signal Two types: Physical: wire cable Wireless: Air T1 lines destinati on T3 network lines server T1 lines T1 lines PHYSICAL TRANSMISSION MEDIA A tangible media Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc. Twisted-pair cable: One or more twisted wires bundled together Made of copper Coax-Cable: Consists of single copper wire surrounded by three layers of insulating and metal materials Typically used for cable TV Fiber-optics: Strands of glass or plastic used to transmit light Very high capacity, low noise, small size, less suitable to natural disturbances PHYSICAL TRANSMISSION MEDIA twisted-pair cable woven or braided metal plastic outer coating copper wire insulating material optical fiber core glass cladding protective coating twisted-pair wire THE ELECTROMAGNETIC SPECTRUM Frequency and wavelength. (a) One cycle. (b) One wavelength. THE ELECTROMAGNETIC SPECTRUM Frequency and Wavelength: Wavelength Wavelength (λ) = speed of light ÷ frequency Speed of light = 3 × 108 meters/second Therefore: λ = 3 × 108 / f Example: What is the wavelength if the frequency is 4MHz? λ = 3 × 108 / 4 MHz = 75 meters (m) GAIN, ATTENUATION, AND DECIBELS Most circuits in electronic communication are used to manipulate signals to produce a desired result. All signal processing circuits involve: Gain Attenuation GAIN, ATTENUATION, AND DECIBELS Gain Gain means amplification. It is the ratio of a circuit’s output to its input. AV = output input An amplifier has gain. = Vout Vin GAIN, ATTENUATION, AND DECIBELS Most amplifiers are also power amplifiers, so the same procedure can be used to calculate power gain AP where Pin is the power input and Pout is the power output. Power gain (Ap) = Pout / Pin Example: The power output of an amplifier is 6 watts (W). The power gain is 80. What is the input power? Ap = Pout / Pin therefore Pin = Pout / Ap Pin = 6 / 80 = 0.075 W = 75 mW GAIN, ATTENUATION, AND DECIBELS An amplifier is cascaded when two or more stages are connected together. The overall gain is the product of the individual circuit gains. Example: Three cascaded amplifiers have power gains of 5, 2, and 17. The input power is 40 mW. What is the output power? Ap = A1 × A2 × A3 = 5 × 2 × 17 = 170 Ap = Pout / Pin therefore Pout = ApPin Pout = 170 (40 × 10-3) = 6.8W GAIN, ATTENUATION, AND DECIBELS Attenuation Attenuation refers to a loss introduced by a circuit or component. If the output signal is lower in amplitude than the input, the circuit has loss or attenuation. The letter A is used to represent attenuation Attenuation A = output/input = Vout/Vin Circuits that introduce attenuation have a gain that is less than 1. With cascaded circuits, the total attenuation is the product of the individual attenuations. GAIN, ATTENUATION, AND DECIBELS Total attenuation is the product of individual attenuations of each cascaded circuit. GAIN, ATTENUATION, AND DECIBELS Decibels The decibel (dB) is a unit of measure used to express the gain or loss of a circuit. The decibel was originally created to express hearing response. A decibel is one-tenth of a bel. When gain and attenuation are both converted into decibels, the overall gain or attenuation of a circuit can be computed by adding individual gains or attenuations, expressed in decibels. GAIN, ATTENUATION, AND DECIBELS Decibels: Decibel Calculations Voltage Gain or Attenuation dB = 20 log Vout/ Vin Current Gain or Attenuation dB = 20 log Iout/ Iin Power Gain or Attenuation dB = 10 log Pout/ Pin
